Intermolecular Interactions Involving Heavy Alkenes H(2)Si=TH(2) (T = C, Si, Ge, Sn, Pb) with H(2)O and HCl: Tetrel Bond and Hydrogen Bond

[Image: see text] The intermolecular interactions between the heavy alkenes H(2)Si=TH(2) (T = C, Si, Ge, Sn, Pb) and H(2)O or HCl have been explored at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVDZ level. The various hydrogen bond (HB) and tetrel bond (TB) complexes can be located on the basis of molecular electrostatic potential maps of the isolated monomers. The competition between TB and HB interactions has been investigated through the relaxed potential energy surface scan. The results indicate that the HB complexes become more and more unstable relative to the TB complexes with the increase of the T atomic number, and cannot even retain as a minimum in some cases, for H(2)Si=TH2···H(2)O systems. In contrast, the HB complexes are generally more stable than TB complexes, and the TB complexes exhibit rather weak binding strength, for H(2)Si=TH(2)···HCl systems. The majority of the TB complexes formed between H(2)Si=TH(2) and H(2)O possesses very strong binding strength with covalent characteristics. The noncovalent TB complexes can be divided into two types on the basis of the orbital interactions: π-hole complexes, with binding angles ranging from 91 to 111°, and hybrid σ/π-hole complexes, with binding angles ranging from 130 to 165°. The interplay between different molecular interactions has been explored, and an interesting result is that the covalent TB interaction is significantly abated and becomes noncovalent because of the competitive effect.